This invention relates generally to induction cooking, and more specifically, to an induction cooking surface unit having high efficiency and reduced electrical stresses on the surface unit switching components.
The principle of induction cooking, that is, circulating eddy currents in the surface of a metallic, food-containing utensil with a time-variant magnetic field generated by an induction drive coil positioned adjacent to the utensil, to cause joule losses in the utensil, and hence, utensil heating, is not a recent innovation. Rather, the principle of induction cooking is well known.
Advantageously, induction cooking is more efficient and less hazardous than conventional cooking with gas burners or electric surface units. When a metallic utensil is heated inductively, virtually all the heat is concentrated in the utensil itself and not on the utensil surface as is the case with conventional utensil heating by gas burners or electric surface units. Because the induction surface unit becomes only slightly warm to the touch during operation, the liklihood of injury to a user, should the induction surface unit be contacted during operation, is greatly reduced.
One of the difficulties in implementing induction cooking on a widespread basis has been the low power factor associated with the induction drive coil. This is primarily attributable to the relatively poor coupling between the induction drive coil and the metallic food-containing utensil. Unless the bottom utensil surface is flat, unbroken, and in intimate contact with the induction drive coil, induction drive coil-utensil coupling cannot readily be improved. Therefore, the present invention is concerned with an improved induction surface unit exhibiting high power factor at full output power and reduced radiation of electromagnetic interference, notwithstanding poor induction drive coil-utensil coupling.